The present invention relates to a cross-connecting module and, more particularly, to a cross-connecting module for switching transmission lines of higher orders.
Conventionally, a cross-connecting module of this sort performs cross-connection by using an STS1 signal having an overhead format as illustrated in FIG. 12 as a unit. This STS1 signal is a signal of SONET (Synchronous Optical NETwork) standard.
As in FIG. 12, the overhead of the STS1 signal consists of transport overhead 33 including section overhead 31 and line overhead 32, and path overhead 34.
On the other hand, in cross-connecting an STS3 signal formed by multiplexing three STS (Synchronous Transport Signal) 1 signals and having an overhead format as shown in FIG. 13, this STS3 signal is byte-interleave-demultiplexed into three STS1 signals, and cross-connection is performed for each of these three STS1 signals.
As in FIG. 13, the overhead of the STS3 signal consists of transport overhead 37 including section overhead 35 and line overhead 36.
That is, as depicted in FIG. 10, the start bit of an input STS3 signal is detected by a synchronous circuit 1. On the basis of the start bit thus detected, the STS3 signal is byte-interleave-demultiplexed by a demultiplex circuit 2.
Three STS1 signals obtained by the byte-interleave-demultiplex performed by the demultiplex circuit 2 are stored in elastic memories 3, 4, and 5 for absorbing phase differences and applied to a cross-connecting module 11 via interface circuits 8, 9, and 10, respectively.
Note that each of the interface circuits 8 to 10 also checks, on the basis of bytes H1 and H2 as the pointers of the STS1 signal in FIG. 12, whether the corresponding input STS1 signal can be cross-connected by the cross-connecting module 11.
After being cross-connected by the cross-connecting module 11, the three STS1 signals are transferred to synchronous circuits 15, 16, and 17 via interface circuits 12, 13, and 14, respectively, as in FIG. 11.
The synchronous circuits 15, 16, and 17 detect the start bits of the three STS1 signals and transfer the timings at which the start bits are detected to memories 18, 19, and 20, respectively. Consequently, the STS1 signals that are cross-connected by the cross-connecting module 11 are stored in the memories 18 to 20 on the basis of the start bit detection timings.
The STS1 signals thus stored in the memories 18 to 20 are sequentially read out from the memories 18 to 20 under the control of a read controller 21 and byte-interleave-multiplexed by a multiplexer 26.
The STS1 signal rate is 51.84 Mbps. To increase the efficiency of the transmission, the STS1 signals are multiplexed to the higher rate signal. An STS3 signal formed by multiplexing three STS1 signals.
As illustrated in FIG. 3, in an STS3 signal (to be referred to as a concatenation signal hereinafter) to be processed in this method, the data of each of three STS1 signals described above is handled as single data. Therefore, the bytes H1 and H2 of the pointers of each of the second and third STS1 signals are replaced with bytes H1* and H2* of fixed values, respectively.
The fixed value of the byte H1 is "10010011" [to be referred to as 93(HEX) hereinafter], and the fixed value of the byte H2* is "11111111" [to be referred to as FF(HEX) hereinafter].
In performing data transmission in accordance with the above method, this concatenation signal is byte-interleave-demultiplexed by the demultiplex circuit 2 and stored in the elastic memories 3 to 5 in the same manner as in the above-mentioned processing.
Since, however, the pointers of the second and third STS1 signals which are byte-interleave-demultiplexed by the demultiplex circuit 2 have the bytes H1* and H2* of fixed values, the interface circuits 9 and 10 determine that these pointers exceed a cross-connectable range.
It is therefore impossible to cross-connect the second and third STS1 signals by the cross-connecting module 11.
In the conventional cross-connecting module discussed above, if the signal to be processed is the concatenation signal in which the data of each of three STS1 signals is handled as single data, the interface circuits arranged before the cross-connecting module determine that the pointers of the second and third STS1 signals that are byte-interleave-demultiplexed by the demultiplex circuit exceed the cross-connectable range. Consequently, these signals cannot be cross-connected, and this makes transmission of the concatenation signal impossible.